Feldspar is pretty much never translucent like that though. In some of the pictures it looks like there’s some small white opaque minerals in there (or are those spider eggs?) which could be feldspar or plagioclase or just more opaque quartz.
In some of the pictures it just looks like a very quartz-rich granite (especially that CFL light one) which would mean mostly quartz with a little bit of feldspar and/or plagioclase and then little bits of darker minerals (hornblende, biotite, amphibole, etc.) But in other pictures (especially the wet ones) it looks like it has an almost greasy texture, which would suggest maybe one of the cryptocrystaline silica varieties like chert or flint. Although quartzite often does have a similar luster, but with that you should be able to still see some recognizable grains in it if you look very closely. (Of course this is all assuming the thing is pretty hard. Did you ever try scratching it with glass?)
Can you scratch the surface with a knife? Because in some of those shots it looks more like a calcite or something, based on the crystal angles I can sort of see in this shot. Looks a little like rhomb cleavage. Could be quartz, too, and I’m just seeing things. Try dropping some acid on it - vinegar, lemon juice… If it fizzes, it’s carbonate like calcite.
Those are some terrible shots, BTW - wetting the rock that much just gives a whole lot of highlights and reflections that do nothing to show the rock. If you have to wet a rock to bring up detail, it should just be damp, not dripping. And always, always put something in the shot for scale - pen, coin, lens cap or best of all, a ruler.
Yeah, I know the photos are not good. It’s really hard to get this point-and-shoot to focus on it, since it doesn’t have spot metering. It looks for something with more defined edges and the rock gets blurred out because it’s a macro shot.
No fizzing from vinegar, and I tried to scratch the bathroom mirror without success. Also, the very sharp tip of my pocket knife didn’t seem to make a mark.
If it doesn’t fizz with light muriatic acid, then it looks like quartz. The picture is bad but there seems to be some 2D orientation to it. On closer inspection, does it have the banded texture of chalcedony?
I’m pretty sure it’s a vein or some kind of open space-filling hydrothermal quartz. Zooming in on the wet samples show some breccia-like inclusions. And then, there’s the overall tabular shape.
Looks a lot like your second link, actually. Maybe I’ll dig out my other camera and macro lens today and see if I can get a better shot of it if the sun pokes out.
Looking at these pictures closely I have to agree with the_diego, it’s quartz from a vein. Held over a small bright light it should be clearly translucent.
As far as color in rocks, you have to realize that in quartz, the color usually is from impurities (or in the case of Smoky Quartz, radiation damage). Open up a random geode, and you’ll see quartz of all different colors. If your Quartz were purple, we’d call it Amethyst. If it were yellow or brown, we’d call it Citrine. But it’s simply quartz with different kinds of impurities.
I was a Geophysics major in College – granted that was about 35 years ago, and I did switch to Engineering… But I agree with the quartz verdict.
Must be. I even broke out my DSLR and macro lens and couldn’t get a good shot of it, and I’m a pretty decent photographer. My only explanation is that this is some sort of black hole material that keeps time shifting.